gh-136003: Skip non-daemon threads when exceptions occur during finalization (GH-139129)

During finalization, we need to mark all non-daemon threads as daemon to quickly shut down threads when sending CTRL^C to the process. This was a minor regression from GH-136004.

Lib/test/test_threading.py

@@ -6,7 +6,7 @@ import test.support
 from test.support import threading_helper, requires_subprocess, requires_gil_enabled
 from test.support import verbose, cpython_only, os_helper
 from test.support.import_helper import ensure_lazy_imports, import_module
-from test.support.script_helper import assert_python_ok, assert_python_failure
+from test.support.script_helper import assert_python_ok, assert_python_failure, spawn_python
 from test.support import force_not_colorized
 
 import random
@@ -2083,6 +2083,32 @@ class ThreadingExceptionTests(BaseTestCase):
         self.assertEqual(out, b"")
         self.assertEqual(err, b"")
 
+    @requires_subprocess()
+    @unittest.skipIf(os.name == 'nt', "signals don't work well on windows")
+    def test_keyboard_interrupt_during_threading_shutdown(self):
+        import subprocess
+        source = f"""
+        from threading import Thread
+        import time
+        import os
+
+
+        def test():
+            print('a', flush=True, end='')
+            time.sleep(10)
+
+
+        for _ in range(3):
+            Thread(target=test).start()
+        """
+
+        with spawn_python("-c", source, stderr=subprocess.PIPE) as proc:
+            self.assertEqual(proc.stdout.read(3), b'aaa')
+            proc.send_signal(signal.SIGINT)
+            proc.stderr.flush()
+            error = proc.stderr.read()
+            self.assertIn(b"KeyboardInterrupt", error)
+
 
 class ThreadRunFail(threading.Thread):
     def run(self):

Modules/_threadmodule.c

@@ -2429,10 +2429,8 @@ thread_shutdown(PyObject *self, PyObject *args)
         // Wait for the thread to finish. If we're interrupted, such
         // as by a ctrl-c we print the error and exit early.
         if (ThreadHandle_join(handle, -1) < 0) {
-            PyErr_FormatUnraisable("Exception ignored while joining a thread "
-                                   "in _thread._shutdown()");
             ThreadHandle_decref(handle);
-            Py_RETURN_NONE;
+            return NULL;
         }
 
         ThreadHandle_decref(handle);

Python/pylifecycle.c

@@ -3548,6 +3548,27 @@ Py_ExitStatusException(PyStatus status)
 }
 
 
+static void
+handle_thread_shutdown_exception(PyThreadState *tstate)
+{
+    assert(tstate != NULL);
+    assert(_PyErr_Occurred(tstate));
+    PyInterpreterState *interp = tstate->interp;
+    assert(interp->threads.head != NULL);
+    _PyEval_StopTheWorld(interp);
+
+    // We don't have to worry about locking this because the
+    // world is stopped.
+    _Py_FOR_EACH_TSTATE_UNLOCKED(interp, tstate) {
+        if (tstate->_whence == _PyThreadState_WHENCE_THREADING) {
+            tstate->_whence = _PyThreadState_WHENCE_THREADING_DAEMON;
+        }
+    }
+
+    _PyEval_StartTheWorld(interp);
+    PyErr_FormatUnraisable("Exception ignored on threading shutdown");
+}
+
 /* Wait until threading._shutdown completes, provided
    the threading module was imported in the first place.
    The shutdown routine will wait until all non-daemon
@@ -3559,14 +3580,14 @@ wait_for_thread_shutdown(PyThreadState *tstate)
     PyObject *threading = PyImport_GetModule(&_Py_ID(threading));
     if (threading == NULL) {
         if (_PyErr_Occurred(tstate)) {
-            PyErr_FormatUnraisable("Exception ignored on threading shutdown");
+            handle_thread_shutdown_exception(tstate);
         }
         /* else: threading not imported */
         return;
     }
     result = PyObject_CallMethodNoArgs(threading, &_Py_ID(_shutdown));
     if (result == NULL) {
-        PyErr_FormatUnraisable("Exception ignored on threading shutdown");
+        handle_thread_shutdown_exception(tstate);
     }
     else {
         Py_DECREF(result);